WHAT IS PCB?
A printed circuit board, or PCB, is used to mechanically support and electrically connect electronic components using conductive pathways, tracks or signal traces etched from copper sheets laminated onto a non-conductive substrate.
Types of PCB
· Single sided
· Double sided (PTH) Printed Through Hole
· Multi Layer.
DETAIL ABOUT THE PCB:
Tracks
There is no recommended standard for track sizes. What size track you use will depend upon (in order of important) the electrical requirements of the design, the routing space and clearance you have available, and your own personal preference. Every design will have a different set of electrical requirements which can vary between tracks on the board. All but basic non-critical designs will require a mixture of track sizes. As a general rule though, the bigger the track width, the better. Bigger tracks have lower DC resistance, lower inductance, can be easier and cheaper for the manufacturer to etch, and are easier to inspect and rework.
Pads
Pad sizes, shapes and dimensions will depend not only upon the component you are using, but also the
manufacturing process used to assemble the board, among other things. There are a whole slew of standards
and theories behind pad sizes and layouts, and this will be explained later. Suffice it to say at this stage that
your PCB package should come with a set of basic component libraries that will get you started. For all but the
simplest boards though, you’ll have to modify these basic components to suit your purpose. Over time you will
build up your own library of components suitable for various requirements.
There is an important parameter known as the pad/hole ratio. This is the ratio of the pad size to the hole size.Each manufacturer will have their own minimum specification for this. As a simple rule of thumb, the pad should be at least 1.8 times the diameter of the hole, or at least 0.5mm larger. This is to allow for alignment tolerances on the drill and the artwork on top and bottom layers. This ratio gets more important the smaller the pad and hole become, and is particularly relevant to via.
Clearances
Electrical clearances are an important requirement for all boards. Too tight a clearance between tracks and pads may lead to “hairline” shorts and other etching problems during the manufacturing process.
Clearances for Electrical Conductors
The track size varies with how much voltage is applied, below the table
0-15V 0.05mm
16-30V 0.05mm
31-50V 0.1mm
51-100V 0.1mm
An example of GOOD power routing (Left) and BAD power routing (Right)
Finishing Touches
Once you have finished all your routing, your board isn’t done quite yet. There are a few last minute checks and finishing touches you should do.
Single Sided Design
Single sided design can greatly reduce the cost of your board. If you can fit your design on a single sided board
then it is preferable to do so. Look inside many of today’s consumer items like TV’s and DVD players, and you
will almost certainly find some single sided boards. They are still used because they are so cheap to
manufacture
Double Sided Design
Double sided design gives an extra degree of freedom for designing your board. Things that were next to
impossible on a single sided board become relatively easy when you add an additional layer.
Silkscreen
The “silkscreen” layer is also known as the “component overlay” or “component layer”. It is the layer on the top of your board (and bottom if needed) that contains your component outlines, designators (C1, R1 etc), and free
text.
Solder Mask
A solder mask is a thin polymer coating on your board which surrounds your pads to help prevent solder from
bridging between pins. This is essential for surface mount and fine pitch devices. The solder mask typically
covers everything except pads and vias. Your PCB program will automatically remove solder mask from pads and via
Design Rule Checking
Design Rule Checking (DRC) allows you to automatically check your PCB design for connectivity, clearance,
and other manufacturing errors. With the large and complex PCBs being designed today, it is impractical to
manually check a PCB design. This is where the DRC comes into its own, it is an absolutely essential step in
professional PCB design.
Examples of what you can check with a DRC are:
Ø Circuit connectivity. It checks that every track on your board matches the connectivity of your
schematic.
Ø Electrical clearance. You can check the clearance between tracks, pads, and components.
Soldering
Soldering considerations need to taken into account when laying out your board.
There are three basic soldering techniques - hand, wave.
PCB DESIGNING TUTORIAL/SPC
This tutorial leads you through the design of a PCB using layout software from ExpressPCB, which is freeware available. Before beginning you should make sure your computer has both Express PCB and Express SCH, if not than you should download the software. Before beginning the PCB process, you should come up with the initial design, build it and test it on a breadboard, fix any errors, and determine specific components. It is also useful to have datasheets and dimensions for all of the “special” components such as transistors, ICs, sensors, actuators, etc., on hand. For this tutorial, we will use a drawer burglar alarm circuit, which had the following form after testing on a breadboard:
There are two stages remaining in the process to creating the circuit board. In the first stage, you build the schematic using the ExpressPCB schematic editor. In the second stage you layout the circuit board. It is possible to skip directly to the layout editor. However, doing the schematic first will allow you to link the schematic into the layout editor reducing the probability of error.
Thank you for sharing this informative blog. It will be very helpful for those who wants to design a PCB or consult with the best PCB design services.
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